Packet switching refers to protocols in which messages are broken up into small packets before they are sent. Each packet is transmitted individually across the net and may even follow different routes to the destination. Thus, each packet has header information about the source, destination, packet numbering etc. At the destination, the packets are reassembled into the original message.
Refers to protocols in which messages are divided into packets before they are sent. Each packet is then transmitted individually and can even follow different routes to its destination. Once all the packets forming a message arrive at the destination, they are recompiled into the original message.
There are two important benefits from packet switching.
1. The first and most important benefit is that since packets are short, the communication links between the nodes are only allocated to transferring a single message for a short period of time while transmitting each packet. Longer messages require a series of packets to be sent, but do not require the link to be dedicated between the transmission of each packet. The implication is that packets belonging to other messages may be sent between the packets of the message being sent from A to D. This provides a much fairer sharing of the resources of each of the links.
2. Another benefit of packet switching is known as "pipelining". Pipelining is visible in the figure above. At the time packet 1 is sent from B to C, packet 2 is sent from A to B; packet 1 is sent from C to D while packet 2 is sent from B to C and packet 3 is sent from A to B and so forth. This simultaneous use of communications links represents a gain in efficiency. The total delay for transmission across a packet network may be considerably less than for message switching, despite the inclusion of a header in each packet rather than in each message.
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